Technical Field
The present invention relates to a vehicle control device and, more specifically, to a vehicle control device capable of optionally switching a plurality of traveling modes in different transmission states of an engine output to driving wheels and having an idling stop function for automatically stopping an engine when a vehicle stops and automatically starting the engine in starting the vehicle thereafter.
Related Art
A four-wheel drive vehicle has been spread that distributes an output of an engine to front wheels and rear wheels to improve off-road traveling performance, a low μ road, and the like (hereinafter sometimes generally referred to as rough road as well) and driving both of the front wheels and the rear wheels to travel. For example, a part-time type four-wheel driving vehicle described in Japanese Patent Application Laid-Open No. H4-212635 is configured to distribute an engine output input to a transfer via a sub-reduction gear to a front wheel side and a rear wheel side while allowing a differential motion with a center differential gear. A 2WD/4WD switching mechanism for transmitting or interrupting power is interposed between the center differential gear and the rear wheels. A lock mechanism for limiting the differential motion is attached to the center differential gear.
The 2WD/4WD switching mechanism and the lock mechanism operate according to a traveling mode selected by a driver. For example, when a two-wheel drive mode is selected as the traveling mode, the 2WD/4WD switching mechanism is switched to a disconnected position and the vehicle travels with driving of only the rear wheels. When a four-wheel drive mode is selected, the 2WD/4WD switching mechanism is switched to a connected position, the lock mechanism is switched to an unlock position, and the vehicle travels with driving of the front wheels and the rear wheels in a state in which a differential motion between the front and rear wheels is allowed. When a four-wheel drive lock mode is selected, the 2WD/4WD switching mechanism is switched to the connected position, the lock mechanism is switched to a lock position, and the vehicle travels with driving of the front wheels and the rear wheels in a state in which the differential motion between the front and rear wheels is limited.
On the other hand, in recent years, for the purpose of, for example, improvement of fuel consumption performance, a vehicle including an idling stop function for automatically stopping and automatically starting an engine in waiting for a green light. For example, in techniques described in Japanese Patent Application Laid-Open No. 2012-255383 and Japanese Patent Application Laid-Open No. 2012-255492, an engine is automatically stopped when both of predetermined stop conditions, for example, vehicle speed=0 and brake ON are satisfied and the engine is automatically started when predetermined restart conditions, for example, brake OFF are satisfied in starting the vehicle thereafter.
Incidentally, although the idling stop function is desirable in terms of the fuel efficiency performance, there is some room of improvement from the viewpoint of convenience for a driver, for example, the start of the vehicle is sometimes slightly delayed because of the engine automatic start. It is not completely unlikely that the stopped engine cannot be automatically started, that is, the vehicle falls into a start impossible situation.
Naturally, the idling stop function is sometimes mounted on the four-wheel drive vehicle. Compared with the general two-wheel drive vehicle, the four-wheel drive vehicle is more often used in, for example, traveling on a rough road because of characteristics of the four-wheel drive vehicle. More careful drive operation is required on the rough road than on the general road. Inappropriate drive operation sometimes directly leads to a trouble such as a stuck vehicle. Therefore, if the engine is automatically stopped by the idling stop function in every stop of the vehicle during traveling on such a rough road, it is likely that more important traveling of the vehicle is hindered.
For example, immediately before entering an undulating off-road, the driver often stop the vehicle to learn the forward geography. When the engine is automatically stopped every time the vehicle is stopped, the vehicle cannot be smoothly started. When the vehicle is stuck in a muddy ground, the vehicle needs to be gently started to escape from the stuck state. However, the engine immediately after the automatic start is inappropriate for such drive operation because torque suddenly rises and induces a slip of driving wheels. If the stopped engine cannot be automatically started because of some cause, it is impossible to escape from the stuck state.
In general, the idling stop function can be optionally cancelled by switch operation. However, it is complicated to perform the switch operation every time. A driver who loses peace of mind because of the stuck state or the like sometimes does not notice a countermeasure. There has been a demand for drastic measures on the vehicle side.